The present invention relates to a cellular phone that signals receipt of a call by using a melody, and particularly to a cellular phone suitable to generate receiving sound that comprises of a plurality of tones.
A conventional receiving sound generator of a cellular phone supplies a signal corresponding to a melody stored in a memory to a speaker as it is.
Since smaller size and lighter weight is required of a cellular phone, a speaker for producing receiving sound used in the cellular phone is of small size. Generally, a speaker with a diameter of about 20 mm is used. In such a small-sized speaker, a frequency range is limited to that between a low frequency of about 400 Hz and a high frequency of about 8 kHz. In this frequency range, a range of about 600 Hz to about 5 kHz allows a sufficient level of sound pressure to be generated. Conventionally, when a signal corresponding to a receiving melody is supplied to such a speaker, the inputted signal is not outputted as sound in a range lower than 400 Hz or in a range higher than 8 kHz, and yet only electric power is consumed. On the other hand, the power allowed to be inputted to a speaker includes power consumed in a frequency range where a signal is not outputted as sound. Therefore, if an input signal includes a signal outside of a frequency range of 400 Hz to 8 kHz, the level of the input signal in the frequency range of 400 Hz to 8 kHz needs to be lowered in order to control the input power to within an allowable value. The level of the input signal needs to be controlled to a low level especially when a melody is to be accompanied by a chord, because the chord may include a signal for high-pitched sound or low-pitched sound that falls outside of the frequency range of 400 Hz to 8 kHz. Thus, it has been difficult to increase the volume of receiving sound. In order to solve this problem, supplying an input signal through a bandpass filter has been considered. However, the method of supplying an input signal through a bandpass filter has a problem in that if a melody includes a note having a frequency outside of the frequency range of 400 Hz to 8 kHz, the note is omitted, thereby resulting in an sounding melody. If a melody is accompanied by a chord and one of the chord notes falls outside of the frequency range of 400 Hz to 8 kHz, the chord is not formed, and therefore the sound may be perceived as strange when the melody is heard.